In the same way that we can combine threaded trees with AVL trees to
produce threaded AVL trees, we can combine right-threaded trees with
AVL trees to produce right-threaded AVL trees. This chapter explores
this combination, producing another table implementation.

Here's the form of the source and header files. Notice the use of
rtavl_ as the identifier prefix. Likewise, we will often refer to
right-threaded AVL trees as “RTAVL trees”.